"The extortion is at all levels of the force. If you try to fight it, they cut you down," says the 13-year veteran.

Mr. Perez and another former Mexican cop have been on a hunger strike for a week now. Perez blew the whistle on police malfeasance once before. He says it cost him his job in 1989. Now, he is close to losing his home.

Allegations of extortion, assaults, and robbery by police are nothing new here. But a growing number of former and active officers are breaking the "code of silence." About a dozen officers demonstrated in Mexico City's central plaza last month. Momentum may be gathering for a full investigation of this city's 28,000-member police force.

"This is a new phenomenon," says Amalia Dolores Garcia Mendez, member of the Federal District Assembly and president of the Public Security and Civil Protection Commission. She has received more than 150 complaints from police officers in the last two months. "The citizens have reached their limit. And the police in the streets are sandwiched between angry citizens and their corrupt supervisors demanding more money."

Ex-policeman Ricardo Chaires Coria claims he was kidnapped two weeks ago and threatened for two days by unknown persons. A week later, he and Perez began their hunger strike, which now has been joined by about 20 police-band musicians fired last September after exposing payroll-padding by their director. More significantly, a small but vocal group of active police officers is joining the protest on the median strip of a major boulevard in front of the United States Embassy. 'The bite' is part of everyday life

Collecting bribes, says tow-truck policeman Martin Perez Garduno, goes with the job. "I have no choice. Until six months ago, I had to pay my boss 50,000 pesos ($16.50) a shift. Now it's 100,000 pesos ($33) every eight-hour shift. This has got to stop." Mr. Perez Gardus salary is some 35,000 pesos ($11.50) per day.

It is a rare Mexico City driver or business person who has not felt la mordida or "the bite." Typically, one is pulled over either on a pretext or for a legitimate traffic violation. A bribe is never overtly requested, but every violation seems to require "a trip to the station" to do the paperwork. As "a favor, you can pay your 'fine' now." If you insist on going to the station, generally, the police may argue that it is cheaper to pay the "fine" now, or may simply let you go.

La mordida is so well known and accepted by some, that drivers in a hurry may simply hand a bill out the window when the officer approaches and speed off.

Payments to superiors range from 20,000 to 120,000 pesos ($6.60 to $39.60) per day, officers say. Street cops take their own 10 to 20 percent cut, supervisors take a percentage and pass along a percentage. Motorcycle, tow-truck, and patrol-car posts provide the most opportunity for "extra" income, and these positions may be sold by supervisors for as much as $1,000 - about four times an average police officer's monthly wage.

"We all know there's corruption in the police force. The problem is getting proof to get at the root of the problem," says Maria del Carmen Segura Rangel, president of the city assembly's justice commission.

The solution, according to Ms. Garcia, is a complete overhaul of the police structure. "The requisites now for entry are ridiculous: three photos, minimum height, primary school education, and completion of military service," says Garcia. Higher standards and higher pay are needed. "If they lived on what they're actually paid, they'd live in cardboard boxes in the slums." Critic wants decentralized police

She would decentralize the force with local commanders responsible to specific neighborhoods and local political representatives. "The command structure now is one vertical, solid body of close alliances. A subordinate cannot push a complaint up. The upper ranks all protect each other," Garcia says.

A statement from the office of Mexico City Mayor Manuel Camacho Solis says complaints from 12 to 15 police have been received and an "exhaustive case by case" investigation has begun. It says Perez quit voluntarily and had "behaved inappropriately" in uniform.

Police spokesman Hector Rivera Trujillo says the strikers and their supporters are mostly disgruntled opportunists whose cases have already been settled. And Perez Garduno has talked to the press but not filed a formal complaint, Mr. Rivera says. Perez Garduno has a copy of a complaint he says was filed last month.

"We're running a clean, dignified police force," Rivera says, adding that Perez Gardus boss was fired recently. Of the 2,721 officers that quit or were fired last year, he says, 15 percent were accused of wrongdoing.

But Garcia argues that more needs to be done. "We need a big cultural change.... People say such a change is impossible. But we're reaching the limit of tolerance with this system."